JustRottenFleshToLeather (JRFTL) is a mod that adds multiple ways of obtaining leather from rotten flesh, making this once useless item serve a new purpose!
Currently you can either cook Rotten Flesh in a Furnace or Smoker, or use a Campfire to turn it into leather!
This mod was born due to a lack of Rotten Flesh to Leather mods being updated for more modern versions of the game in a short amount of time (at least for Fabric mods).